1. Field of the Invention
The present invention relates to a lens barrel provided at the front end thereof with a lens barrier mechanism which is driven to open and close its barrier blades for protecting the frontmost lens surface from being stained or damaged.
2. Description of the Related Art
As an example of a conventional lens barrel having a lens barrier mechanism, a lens barrel which is provided therein with a stationary ring, a rotating cam ring positioned inside the stationary ring, and an exterior ring member positioned between the stationary ring and the cam ring, is known in the art. The cam ring is provided with a set of follower pins, and the exterior ring member is provided with a corresponding set of cam grooves in which the set of follower pins of the cam ring are respectively engaged. The lens barrier mechanism having barrier blades driven to open and close a photographing aperture of the lens barrel is fixed to the front end opening of the exterior ring member. Driving the cam ring to rotate in forward and reverse directions causes the exterior ring member to advance and retreat in an optical axis direction while opening and closing the barrier blades of the lens barrier mechanism, respectively.
In such a conventional lens barrel, the diameter of the exterior ring member is preferably as small as possible from a design point of view. On the other hand, in order for the barrier blades to be widely opened to open the photographing aperture widely, the diameter of the lens barrier mechanism needs to be large. However, the inner diameter of the exterior ring member has to be large if the diameter of the lens barrier mechanism is large.
In the case where one or more cam grooves are formed on an inner peripheral surface of the exterior ring member, the wall of the exterior ring member has to be thick because the cam groove generally has a deep radial depth. Accordingly, the inner diameter of the exterior ring member decreases and increases if the outer diameter of the exterior ring member is decreased and increased, respectively.
Although the diameter of the lens barrel is desirably small from a design point of view, with regard to the outward appearance thereof, each barrier blade of the lens barrier mechanism needs to have a long length if it is desired to provide a large photographing aperture which is opened and closed by the lens barrier mechanism. However, the diameter of the lens barrel increases if the length of the barrier blade is increased.
The present invention provides a lens barrel having a lens barrier mechanism fixed to a ring member, wherein the ring member is successfully formed to have a large inner diameter with a minimum increase of the outer diameter of the ring member so that the lens barrier mechanism having a large diameter can be fixed to the ring member. The present invention further provides a lens barrel having a lens barrier mechanism, wherein the lens barrier mechanism fixed to a ring member is successfully provided with a set of long barrier blades without an increase of the diameter of the ring member and without complicating the structure of the lens barrier mechanism.
For example, in an embodiment, a lens barrel is provided, including a stationary barrel, an outer ring, an inner ring, a cam ring and a movable lens frame, arranged in that order from outermost side, wherein the axes thereof coincide with a common optical axis, the outer ring being guided linearly in the optical axis direction by the stationary barrel, the inner ring being linearly guided in the optical axis direction by the outer ring via a linear guide key and a linear guide groove provided on one and the other of said inner ring and said outer ring, respectively, the cam ring being rotatable to move the movable lens frame in the optical axis direction; and a lens barrier mechanism having an aperture positioned in front of the movable lens frame, the lens barrier mechanism being provided on a front opening of the inner ring, for opening and closing the aperture.
The outer ring can be linearly guided in the optical axis direction relative to the stationary barrel via a linear guide key and a linear guide groove provided on one and other of the outer ring and the stationary barrel, respectively.
The cam ring can include a thick-wall cylinder portion and a circumferential groove provided in front of the thick-wall cylinder portion. The outer ring can include projections formed at a rear end portion of the outer ring to be engaged in the circumferential groove to be rotatable about the optical axis along the circumferential groove, whereby the cam ring is movable in the optical axis direction together with the outer ring.
The cam ring can include at least one first cam groove and at least one second cam groove formed on inner and outer surfaces of the cam ring, respectively, the lens barrel further including a first cam mechanism for moving the movable lens frame forward from the cam ring in the optical axis direction by the rotation of the cam ring in accordance with a profile of the first cam groove; and a second cam mechanism for moving the inner ring in the optical axis direction by rotation of the cam ring in accordance with a profile of the second cam groove.
The profile of the first cam groove and the profile of the second cam groove can be formed so as to move the movable lens frame and the inner ring while maintaining a substantially constant distance therebetween in the optical axis direction.
The lens barrier mechanism can include a pair of barrier blades driven to open and close the aperture; and a drive ring driven to rotate about the optical axis to drive the pair of barrier blades to open and close the aperture, the drive ring having at least one engaging surface. The cam ring can include at least one rotation transfer face formed at a front end of the cam ring to extend parallel to the optical axis, the rotation transfer face coming into contact with corresponding the engaging surface of the drive ring to rotate the drive ring. A portion of at least one of the first cam groove and the second cam groove extends in front of a rearward edge of the rotation transfer face in the optical axis direction.
The drive ring can include at least one recess, the engaging surface of the drive ring being formed as one surface of the recess.
The cam ring can include at least one recess formed at the front end of the cam ring at portions other than portions of the cam ring on which the first cam groove and the at least second cam groove are formed, the rotation transfer face of the cam ring constituting one surface of the recess.
It is desirable for the inner ring and the outer ring to be movable between respective accommodation positions and respective advanced positions in front of the respective accommodation positions. The inner ring can include an opening which corresponds with the rotation transfer face of the cam ring. The rotation transfer face of the cam ring extends through the inner ring via the opening of the inner ring to come in contact with corresponding the engaging surface of the drive ring when the inner ring and the outer ring are positioned in the respective accommodation positions.
The lens barrel can be a zoom lens barrel.
The thick-wall cylinder portion can be formed at a rear end of the cam ring, the circumferential groove being formed on an outer peripheral surface of the cam ring immediately in front of the thick-wall cylinder portion, and the projections extending radially inwards to be engaged in the circumferential groove.
The second cam mechanism can move the inner ring forward in the optical axis direction relative to the cam ring via the rotation of the cam ring in accordance with the profile of the second cam groove.
It is desirable for the recess to be formed on an outer peripheral surface of the drive ring.
In another embodiment, a lens barrel is provided, having a lens barrier mechanism for opening and closing an aperture in front of a lens group, the lens barrier mechanism being fixed to a front end of a ring member provided around the lens group, the lens barrier mechanism including a pair of barrier blades each of which is rotatable about a pivot in order to open and close the aperture; and a pair of recesses formed on an inner periphery of the ring member so as to allow the pair of barrier blades to partly enter the pair of recesses, respectively, when the pair of barriers fully open said aperture.
It is desirable for at least part of the ring member to be formed as synthetic resin.
The ring member can include a main ring body made of synthetic resin; and a metal reinforcing ring fitted on the main ring body to be fixed thereto; wherein the pair of recesses are formed on the main ring body. A radially outermost position at a free end of each the pair of barrier blades is defined by an inner peripheral surface of the reinforcing ring.
The lens barrier mechanism can further include a front end exterior plate on which the aperture is formed, each the pivot projecting rearward from a rear surface of the front exterior plate.
The lens barrel can be an extendable lens barrel.
In another embodiment, a photographing lens barrel is provided, including a pivoted barrier blade driven to open and close a photographing aperture in front of a front lens group; a ring member provided around the lens group, the pivoted barrier blade being supported by a front portion of the ring member; and a recess formed on the ring member so as to allow the barrier blade to partly enter the recess.
The present disclosure relates to subject matter contained in Japanese Patent Applications Nos. 2001-83265 and 2001-83690 (both filed on Mar. 22, 2001) which are expressly incorporated herein by reference in their entireties.